"Schertz, William W." wrote:

Paul,
There was a lot of traffic about the coolant flows for water vs. ethylene
glycol mixes, and I think some numbers didn't add up.

A while back I sent a scanned chart of heat transfer properties for 27
different fluids. I have re-attached it with this message.

Water has a specific heat of 1.0 Btu/lb F,
50/50 water/ethylene glycol has a specific heat of 0.87 Btu/lb F (not .5 as
stated in a previous post)

50/50 water/glycol also has  a poor thermal conductivity, but is still
better than any of the other oils shown in the table.

For what it's worth.

WWS

Bill Freeman wrote:

Thermal conductivity is of minor importance for a heat exchange liquid
which is flowing in a turbulent flow.  The primary heat transfer resistances
from the engine to the air are the convective heat transfer coefficients
from the metal to the liquid and vice versa.  This is what Jeff was pointing
our in his nucleat boiling comments.  The point is that you can't transfer
enough heat from the rotor housing to the coolant without local boiling.
The bubble of coolant vapor forms (absorbing a HUGE amount of
energy in phase change) and then as it is swirled away from the heat
source it immediately recondenses in the cooler fluid stream (dumping a
HUGE amount of energy by phase change).  This process gives MUCH
higher heat transfer than normal turbulent flow convection can support.

Conduction would only be of first order importance if you were in
a static situation.

Bill

 
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